1. Field of the Invention
The present invention relates to a print paper feeding apparatus adapted to be mounted on a printer when in use.
2. Description of the Related Art
Conventional print paper feeding devices of this type are disclosed in Published Unexamined Japanese Patent Applications Nos. 62-111848 and 63-288833. The mechanism disclosed in the latter publication comprises a gear for driving a platen, a gear for driving a paper feed roller, a gear for driving a supplemental feed roller, and a planetary gear mechanism including two sets of sun gears and planetary gears. When the platen is rotated in the forward direction by a paper feeding motor, one of the planetary gears is engaged with the supplemental-feed roller drive gear and the feed-roller drive gear. Thus, rotation of the platen drive gear, which rotates together with the platen, is transmitted as rotation in the paper feeding direction to the mentioned two types of feed rollers. The rotation of both feed rollers and the rotation of the platen feeds a sheet paper toward the print section located in front of the platen.
When the platen is rotated in the reverse direction, the other planetary gear is engaged only with the supplemental-feed roller drive gear, transmitting the rotation of the platen drive gear as rotation in the paper feeding direction only to the supplemental feed roller, not to the paper feed roller.
With the above mechanism, the supplemental-roller drive gear is linked via the planetary gear mechanism to the platen drive gear. Therefore, when jamming of a sheet paper occurs between the supplemental feed roller and the platen, the jammed paper should be pulled out by an operator in a direction opposite to the paper feeding direction. However, the load of the paper feeding motor and the load of the gears are applied to the supplemental feed roller. This makes it difficult for the operator to pull out the paper. Forcibly pulling out the paper is likely to tear the paper or damage the gears.
As a solution to this shortcoming, the printer body is provided with a switching mechanism for selectively transmitting the power of a drive source to either a continuous paper feeder or a sheet paper feeder. The printer body is further provided with a releasing mechanism for disengaging the planetary gear mechanism from the aforementioned supplemental-feed roller drive gear and the feed-roller drive gear in a manner interlocked with the operation of the switching mechanism. When paper jamming occurs, the planetary gear mechanism is disengaged from these two drive gears to free the supplemental feed roller. Thus, the jammed paper can be pulled out in a direction opposite to the paper feeding direction to be removed from the printer body.
The releasing mechanism is designed to interlock with the switching mechanism of the printer body, thus complicating the overall structure of the print paper feeding apparatus.
In addition, the above paper feeding apparatus keeps the paper feed roller in constant abutment with the paper, and has no mechanism to set the feed roller free. Thus, when jammed paper is pulled in the direction opposite to the paper feeding direction, a load acting against the pulling action is applied, making it difficult to pull out the paper.
In the above apparatus, a pair of supplemental feed rollers abut against each other and always rotate during the paper feed. In other words, even in the case where continuous paper or manually-feed paper is in use and the rotation of the supplemental feed rollers is unnecessary, the supplemental feed rollers rotate and thus wear out quickly.
According to the apparatus disclosed in publication No. 63-28833, a sheet of paper is fed toward the platen via the supplemental feed rollers from the paper feed roller by the reverse rotation of the platen. When the paper sheet is caught between the supplemental feed rollers, the platen starts rotating in the forward direction. At this time, the paper feed roller is stopped and the supplemental feed rollers keep rotating to feed the paper. As a result, the paper sheet is fed by the supplemental feed rollers alone and is pulled a specific amount or length between the platen and a pinch roller located behind the platen. Then, the platen rotates in the reverse direction by an amount corresponding to the length of the paper caught, rotating the paper feed roller in the paper feeding direction. This rotation, together with the urging force in the paper feeding direction produced by the supplemental feed rollers and paper feed roller, causes the sheet paper to slack. This causes the front edge of the paper to lie on the surface of the platen in an orientation parallel to the axial direction of the platen shaft. The platen then starts rotating forwardly again, feeding the sheet paper in the print section of the printer.
In this manner, the front edge of the sheet paper is aligned in parallel to the axial direction of the platen shaft on the platen surface. This alignment is called "oblique compensation." This oblique compensation allows the sheet paper to be fed to the print section so that printing is done on the proper position on this paper.
According to the above-described apparatus, when the platen rotates forwardly, its rotation is not transmitted to the paper feed roller. At this time, the rear portion of the sheet paper is caught between the paper feed roller and the top of a stack of sheet papers on a hopper. Since the force of the paper feed roller pressing the stack of the sheet papers is relatively strong, a load is applied to the feeding of the sheet paper by the supplemental feed rollers when the paper feed roller stops rotating. As a result, the supplemental feed rollers can slip on the sheet paper in this apparatus, preventing the paper from having the proper slack. This slippage can cause the sheet paper to move obliquely, thereby preventing the front edge of the paper from accurately reaching the print section.
Another print paper feeding apparatus adapted to be mounted on a printer is disclosed in Published Unexamined Japanese Patent Application Serial No. 62-111848. The disclosed apparatus feeds sheets of paper one by one from a hopper by the paper feed roller in the same manner as described above. The paper is then held between a pair of the supplemental feed rollers and is fed in that state. The supplemental feed rollers are pressed against each other in order to hold the paper as in the case of the apparatus disclosed in the aforementioned publication No. 63-288833.
Supplemental roller shafts to support respective supplemental feed rollers rotatable are supported at both ends by the side frames of the print paper feeding apparatus, causing a slack at the center of each supplemental roller shaft. As the paper feeding is repeated, therefore, the interval between the supplemental roller shafts becomes wider particularly from their center portions, making a gap between the supplemental roller shafts at the respective ends of the supplemental feed rollers. This gap reduces the pressing force between the supplemental feed rollers and make the paper-feeding force insufficient.
In a case of feeding a paper only by the supplemental feed rollers with the paper feed roller not rotating, the supplemental feed rollers require large paper-feeding force. It is not therefore possible to surely feed the paper in that condition, causing a skew or paper jamming.